The present application claims priority under 35 U.S.C. xc2xa7 119 of Korean Application No. 2002-58453, which was filed on Sep. 26, 2002, and Korea Application No. 2002-61856, which was filed Oct. 10, 2002, the disclosures of which are expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an apparatus for measuring magnetic flux of a synchronous reluctance motor and a sensorless control system for such a motor. More particularly, the present invention relates to an apparatus for measuring magnetic flux of a synchronous reluctance motor, whereby higher harmonic components, which are caused by loads generated in the motor when the motor operates, can be removed in measuring magnetic flux of the motor so as to achieve a more accurate flux measurement. The present invention also relates to a sensorless control system of a synchronous reluctance motor for estimating a speed and a rotation angle of a rotor of a synchronous reluctance motor without using a sensor. With this system it is possible to reduce errors in estimating the speed and rotation angle when the motor starts or operates at a low speed and thereby to better stabilize the system.
2. Description of the Related Art
The synchronous reluctance motor refers to a motor in which the driving source of a rotor is synchronized with the driving source of a stator and the rotor is rotated in such a manner that a magnetic resistance formed in the rotor when a current flows into the stator is minimized. It is necessary to know the position of the rotor in order to control a speed of the synchronous reluctance motor. For example, the position of the rotor can be directly detected with a rotor position detector such as an encoder in order to control the motor speed. However, it is difficult to incorporate such an encoder into devices such as the compressor of a refrigerator or an air conditioner.
Thus, a sensorless control system has recently been used, which does not require the use of the rotor position detector. The sensorless control system obtains an estimated magnetic flux and an observed magnetic flux of the motor based on a voltage and a current for driving the motor, and estimates the speed and rotation angle of the rotor based on the estimated magneticflux.
Among such synchronous reluctance motors, a concentric-winding reluctance motor as shown in FIG. 1 can be easily manufactured at a lower cost, relative to a distributed-winding reluctance motor. However, as shown in this figure, spaces between slots 3 of a stator 1 in the concentric-winding reluctance motor are so wide that six harmonic components are included in currents in the motor when a rotor 2 rotates.
FIG. 2 shows graphs of four values, i.e., a trigonometric function value (sin xcex8), a trigonometric function value (sin {tilde over (xcex8)}), a current (iq), and a current (iv). The trigonometric function value (sin xcex8) represents a real rotation angle of the rotor obtained by the encoder as a position detector. The trigonometric function value (sin {tilde over (xcex8)}) represents an estimated rotation angle of the rotor which is obtained based on the magnetic flux in the conventional motor speed control system. The current (iq) represents a q-axis current in a rotational coordinate system which is converted from an input current of the motor, and the current (iv) represents one of the actual three-phase currents which flow in the motor.
As mentioned above, referring to FIG. 1, the spaces between the slots 3 of the stator 1 in the concentric-winding reluctance motor are so wide that six harmonic components are included in the actual V-phase current that flows in the motor. Accordingly, the harmonic components are included also in the q-axis current in the rotational coordinate system. This results in a failure to obtain a sinusoidal wave correctly representing the estimated rotation angle of the rotor, while generating ripple phenomena. Such an error in estimating the rotation angle of the rotor by the speed control system lowers the accuracy and stability of the sensorless control system.
The sensorless control system of the synchronous reluctance motor, which obtains the position of the rotor without using a sensor as mentioned above, uses a first control mode as follows. In the first control mode, the speed and the rotation angle or position (hereinafter, xe2x80x9cpositionxe2x80x9d is also referred to as xe2x80x9crotation anglexe2x80x9d) of the rotor is obtained by measuring a voltage applied to or a current flowing into the motor, or a magnetic flux induced in the motor by the voltage and current. That is, in the first control mode, the speed and rotation of the motor is estimated based on the magnetic flux measured by a flux observer.
However, when the motor starts or operates at a low speed, a problem occurs in estimating the voltage by the flux observer, thereby causing a significant difference between the estimated values and the real values of the speed and rotation angle of the rotor.
Thus, when the motor starts or operates at a low speed, a second control mode has been used, combined with the first control mode, to prevent the estimation errors by injecting an additional signal into the flux observer. Use of the second control mode also causes the following problem. Since the determination on whether to use the second control mode is made based on the speed of the motor, the system stability is lowered at a time when the sensorless control system changes the control mode from the first control mode to the second control mode according to the speed of the motor.
In other words, when the estimated speed of the motor reaches a predetermined speed after the motor starts, the control system abruptly changes the control mode from the second control mode, which has been used during the low speed operation, to the first control mode, thereby causing instabilities such as chattering.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus for measuring magnetic flux of a synchronous reluctance motor, whereby it is possible to measure a magnetic flux from which higher harmonic components caused by loads formed in the motor are removed. The resulting more accurate measurement will improve the performance of a system for controlling a concentric-winding synchronous reluctance motor.
It is another object of the present invention to provide a sensorless control system of a synchronous reluctance motor. In controlling the synchronous reluctance motor without using a sensor, it is possible to prevent instabilities such as chattering when the motor operates at a low or high speed and thereby to stably estimate and measure the speed and rotation angle of the rotor of the motor.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an apparatus for measuring a magnetic flux of a synchronous reluctance motor.
The apparatus includes flux output estimator that estimates a flux of a synchronous reluctance motor by removing higher harmonic components of a current in a rotational coordinate system which flows into the motor.
The apparatus further includes a flux measurer that measures a flux in a fixed coordinate system by combining a voltage in the fixed coordinate system, which is applied to the motor, and a current in the fixed coordinate system, from which higher harmonic components are removed, with the estimated flux outputted from the flux outputestimator.
Finally the apparatus includes a fixed/rotational coordinate converter for converting the measured flux outputted from the flux output estimator to a measured flux in the rotational coordinate system.
In accordance with another aspect of the present invention, there is provided a sensorless control system of a synchronous reluctance motor.
The system includes a sensorless control block for measuring a magnetic flux of a synchronous reluctance motor and estimating a rotation angle and speed of the motor based on the measured flux in order to perform a sensorless control of the motor.
The system further having a low-speed-region tracking loop unit, which is activated or not based on the estimated speed of the motor, for measuring the rotation angle and speed of a rotor of the motor so as to compensate the estimated rotation angle and the estimated speed of the sensorless control block.
Finally the system has a mode switching controller for controlling whether to activate the low-speed-region tracking loop unit based on the estimated speed, and stabilizing chattering phenomena caused by the turning on or off of the low-speed-region tracking loop unit.